Charged MPs planning to use the antiquated law of parliamentary privilege are clutching at straws.

The law, in the 1689 Bill of Rights, was enacted to protect Parliamentarians from arrest in the course of their duties.

In the dark days after the English civil war no one in the fragile House of Commons wanted to risk losing his head.

It was seen as a vital measure to allow MPs to stand up to dictators and other powerful forces in the land.

Parliament's right to have sole control over its affairs, known as exclusive jurisdiction, was also designed to protect MPs' independence and ensure good legislation.

But the rules that allow politicians to speak frankly and fearlessly were never meant to extend beyond Parliament.

There is no immunity from prosecution for politicians and it should not start now.

Even an attempt to use an ancient right as a defence shows the arrogance of MPs.

So used to the "culture of deference" in Westminster, many believe they are untouchable.

They see themselves as lords of the manor rather than servants to the public.

The Director of Public Prosecutions Keir Starmer wants the principle of parliamentary privilege to be tested before a jury. Most observers doubt whether any jury would be persuaded parliamentary privilege is a defence that would apply.

But it has been used successfully in the past - like the time Sir Ian Blair was stopped by parliamentary authorities from investigating the expenses claims of Tory MP Derek Conway.

Now it remains to be seen whether anyone will try to invoke it again - and whether it will carry any weight.

The worst thing is that it could ultimately be left to MPs to change the law to end the abuse of an ancient right.